Bipolar devices are, by now, well known for use in ophthalmic and other surgical procedures. Such devices include two isolated electrodes which are placed in contact with a field of tissue to be treated. The electrodes are coupled with a power supply which passes an electric current through the electrodes and tissue contacted by the electrodes.
Applicant's U.S. Pat. No. 4,476,862, identified above, describes an earlier bipolar probe device and its use for scleral marking. The described embodiment includes a coaxial bipolar electrode assembly with an outer tubular electrode coaxially surrounding an inner axial electrode. The working tip of the probe device may be bent away from a center line of the major portion of the coaxial assembly for ease of use but remain coaxial at the tip which is applied to the tissue field. In the described embodiment, current flows uniformly in all radial directions between the axial electrode and the coaxial surrounding tubular electrode. This configuration provides a rapid reduction of the current density away from the axial electrode, and allows the generation of a small uniform charpoint in the sclera without cutting through the sclera.
Another bipolar ophthalmic device in U.S. Pat. No. 4,548,207 to Reimels includes a probe electrode assembly with a tubular outer electrode and coaxial central electrode. The end of the probe is beveled at an angle of about 45.degree. to the central axis of the probe assembly. The central electrode is relatively large in comparison to the overall electrode assembly and effectively reduces current density around the central electrode. This device is designed particularly for coagulation of blood vessels and/or tissue and is less apt to cauterize sufficiently to cut than is applicant's own earlier embodiments.
U.S. Pat. No. 4,301,802 to Poler describes a cauterizing tool for ophthalmic surgery including anterior capsulotomy. The tool is provided by means of a modified hypodermic syringe needle. The tip of the needle is turned at an approximately 90.degree. angle. An insulated fine wire is passed through the needle portion and turned tip and protrudes substantially coaxially with the end of the turned tip. Like the previous devices, current density would be concentrated around the central electrode but drop away substantial uniformly in all radial directions because of the coaxial orientation of the surrounding electrode formed by the needle.
U.S. Pat. No. 4,483,338 to Bloom et al and related UK application GB No. 2 101 893 describe yet another bipolar electrocauterizing needle embodiment including a perfectly straight outer cylindrical electrode and a coaxially positioned inner electrode. The end of this bipolar electrode needle may be conical frustoconical or perfectly blunt. These would all appear to provide uniform radial current densities around the center electrode.
A number of other references disclose similar, uniformly radially symmetric tubular outer electrode and coaxial inner electrode assemblies. See, for example, "Experimental Intraocular Coagulation", OPHTHALMIC SURGERY, January-February 1972, Vol. 3, No. 1 pp. 32-37; U.S. Pat. No. 2,275,167 to Bierman; U.S. Pat. No. 4,034,762 to Casens et al; "Vas Cautery: Battery - Powered Instrument For Vasectomy", Schmidt et al, UROLOGY Volume III, No. 5, May, 1974, pp. 604-605; An Electro Cautery Instrument For The Fulguration Of The Vas Deferens During Vasectomy For Sterilization", Decker et al, "ISA REPRINT, ISA BM 73302, pp. 5-10, 1973. The latter three references relate to devices inserted into the male vas for sterilization. In each of these devices, as with those previously mentioned, a tubular electrode and coaxially located central electrode is provided causing the aforementioned rapid reduction in current density substantially uniformly around the central, axial electrode.
Other bipolar probe configurations are known. For example, U.S. Pat. No. 3,920,021 to Hiltebrandt has, in addition to a coaxial concentric configuration like those previously discussed, several embodiments in which the center electrode mushrooms from the end of a tubular electrode in a hemispheral dome having an outer diameter equal to that of the tubular electrodes. Such a large "central" electrode would appear to reduce current densities even more than previously discussed embodiments. Another bipolar electrode embodiment includes a pair of semi-circular electrodes. The cord side of the electrodes are adjoining and uniformly spaced from one another. This configuration provides a uniform current density over a relatively wide area between the cord surfaces and lesser current densities between the arcuate surfaces. U.S. Pat. No. 1,983,669 to Kimble teaches a similar configuration of different construction.
U.S. Pat. No. 1,814,791 to Ende describes a bipolar probe device with a pair of parallel spaced axially extending electrodes which can be exposed to varying degrees for different lengths of cervical canal coagulation. It is believed that a substantially uniform current density is also provided between the exposed lengths of electrode.
Lastly, U.S. Pat. No. 3,987,795 to Morrison describes a number of sesqipolar electrode devices particularly suited for cutting and heavy coagulation applications. Not only are these devices too large for ophthalmic use, the arcing they are designed to provide is likely to cause injury to the optic nerve and other tissue of the eye.
None of the foregoing configurations, is believed optimal for anterior capsule cutting. That procedure requires the provision of sufficient current density to coagulate the anterior capsule and, preferably, the immediately underlining cortex, but currents and voltages sufficiently small so as to avoid optic nerve and other undesired tissue damage.